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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5948_Библиотеки_им_академика_М_И_Перельмана
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Arm to finger 17.5 + 4.4
Arm to ear 8 – 14
Lung to ear 3 – 5
Rigjt ventricle to Left ventricle 2 – 4
Intravenous route means no absorption step is there. There is no physiological factor which
can affect the absorption. Among various sites of human body, the intravenous circulation
time is maximum about 25 sec when the drug reaches toe from arm as shown in Table 1.12.
Depending on the property of the drug injected and the site of action, the actual onset of
action of a drug varies.
Extravascular route is used to inject a drug. The speed at which the drug enters the blood
stream can vary greatly and is influenced by a number of physiological factors. For
absorption, a fraction of drug present in solution is required to be transferred through the
capillary wall membrane. It is thought that drugs are absorbed only through this mechanism.
No evidence has been reported indicating the ability for drugs to become absorbed directly
through the walls of the larger blood vessels.
The capillary cell membrane is very thin and elastic, 75 – 100 Å(1Å = 1×10
–8
cm). The
elastic material contains about 55% of proteins, 40% of lipid, and 5% of polysaccharide
substances
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. However, its exact molecular structure is not uncertain. It is considered that a
central layer of lipids is covered by protein layers and then a thin layer of polysaccharide
substance covers the outer surface. The central lipid layer makes it impermeable to lipid
insoluble substances. This is a significant factor for diffusion of drugs extra vascularly
injected. However, very small lipid-insoluble substances such as water and urea can pass
through the capillary membrane. These can pass through pores by a process of filtration. The
concentration gradient is the driving force. Since the drug does not leave the aqueous
solution during filtration, physicochemical factors such as pKa and partition coefficient do
not influence the rate of transport. The pores are only about 30Å in radius and total area is
less than about 0.1% area of the capillary wall. This process is considered insignificant to the
overall membrane transfer process because of its small size.
Anatomical characteristics
Anatomical characteristics of the extravascular injection site considerably influence the rate
of absorption of a drug. The surface area available for absorption depends on the number of
capillaries at the site. If the number of capillaries is more, greater surface area would be
available and more absorption will occur.
Muscle movement
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Muscle movement is directly related to the rate of flow through lymphatic vessels. This can
be demonstrated by injecting the rabbits subcutaneously. It has been seen that when venom
was injected with immobilized limb, it took about 8 hrs to cause death, where as
unrestrained rabbits died in 2.5 hr. Absorption of drug increases with increased activity or
increased blood flow. Muscular contraction occurs during exercise increases both dispersion
of drug and local blood flow. Muscle becomes more vascular than subcutaneous tissue;
hence uptake becomes faster.
Tissue condition
Tissue condition indicates the tissue vascularity and hence, affects the absorption of drug. In
other words, changes in tissue vascularity caused by scarring can influence the drug
absorption. In rabbits the rate of clearance of hippuran became slow when injection was
given at a site, previously mechanically traumatized by injecting sodium chloride injection
twice daily for a week. Scar tissue can be formed by injecting at one site repeatedly. Rotation
of injection sites can provide more favorable absorption in maintaining good absorption of a
drug.
Body temperature
Body temperature is also directly related to the rate of absorption of a drug, as does the rate
of metabolism and most other physical and chemical reactions. It is considered that both
diffusion and blood flow, and other physiological activities, can be affected by changes in
body temperature. Generally, vasoconstriction takes place during the seasons when external
temperature is cold. This is the way how the body reduces the loss of heat through surface
vessels. On the other hand, during summer when external temperature is more, vasodilation
occurs. However, the amount of body temperature changes from normal is usually not so
important or controllable factor for designing of a dosage form. Application of heat at the
site of injection definitely causes faster absorption due to local vasodilation.
Age of the patient
The factors such as reduced adipose tissue, lower renal clearance are related to the age.
However, the effect of age on the absorption of drug from injection sites is not well known,
and whether these factors play a definite role is not certain also. Reduced adipose tissue
causes a greater availability of drug to the systemic circulation because the ability of
retention of drug by such tissue is reduced, particularly if the drug has a high partition
coefficient. Usually, lower drug-blood level is found in neonates and children than in adults
when the drug is injected based on 1 mg/kg of body weight. This is attributed to high
volumes of distribution of drug into body tissues other than blood. This is due to greater
relative amounts of total body water per kilogram of body weight in neonates compared to
adults
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. It has been suggested that the thickness and composition of subcutaneous adipose
tissue may change with age. May be for this reason, partition coefficient in younger and
older tissues changes and there would be variation in absorption of drug. This has also been
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observed that relative percentages of C12 to C18 triglycerides between adult and children
showed marked difference; this further supports the possibility changes in subcutaneous
adipose tissue with age.
Disease state
Absorption of penicillin G from the intramuscular injection site is reduced in case aqueous
suspension of penicillin G is injected to patients suffered from heart failure. This can be
justified by the fact that a damaged heart cannot pump blood as efficiently as a healthy heart;
thus, volumes of blood available for absorption of drug are different. In another study, it has
been found that the metabolic function of cancer cells is higher than normal cells; for this
reason, when intravenous or intra-articular injection of methotrexate is administered, drug
tissue level is much lower in cancer patients than in normal patients. Thus, rapid metabolism
of drug lowers the drug tissue level in cancer patients.
Mediator enzymes
The onset of drug absorption is increased by the enzymes hyaluronidase, even when a drug
is administered through intramuscular injection, is a known fact. This enzyme hydrolyzes
hyaluronic acid, a component of tissue ground substance. This controls the spread of fluids
at the site of injection. After hydrolysis the area of drug distribution in the tissue is increased
and as a result, the absorption rate is also increased. Chymotrypsin can increase the rate of
elimination of tetracycline from the body from 13% to 37%, the actual mechanism for such
effect is not known.
Vasoactive agents
Epinephrine has been found to influence the rate of absorption of radioactive
24
Na
administered subcutaneously. Epinephrine constricts the local blood vessels present in the
area of absorption. As a result, the blood flow is reduced and absorption of drug is also
reduced. When epinephrine is co-administered with benzyl penicillin solution, absorption
would be significantly reduced. This principle has been used particularly for the
administration of local anesthetics. Similarly, it was found that when prostaglandin E2 was
co-administered, its vasodilating effect increased the blood flow and increased absorption of
benzyl penicillin
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.
Formulation Consideration
There are various factors which are to be considered during formulation development of
injectables to distribute the drug effectively when the drug is administered through
subcutaneous and intramuscular injection.
Solubility of drug
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1.
2.
3.
4.
The drugs should be completely solubilized before they penetrate the muscle or tissue
barriers and enter the circulatory system. Two types of solubility are important – (1)
solubility in the vehicle of the dosage form, and (2) solubility in body fluids.
For drugs administered as solution, dosage form solubility is avoided. However, for drugs
administered as suspensions, the rate of dissolution of drug from the dosage form vehicle,
and the rate of dissolution in tissue fluids at the injection site, mainly determines the rate of
absorption of the drug. The dissolution rate of injected drug suspensions depend on
The size of drug particles,
pH of the fluids at injection site,
The polymorphic character of the drug crystals, and
The diffusion coefficient of the drug.
At the higher viscosities the diffusion coefficient of the drug is less. Once the drug goes into
solution from the dosage form, its solubility in fluids in the subcutaneous tissues or muscles
depends on its partition coefficient and its degree of ionization as per the pH of the fluids
present at the site of injection.
Partition coefficient of the drug
If the drug is less soluble in lipids, its partition coefficient will be less. Thus, the absorption
of the drug into the blood stream from the site of injection would also be slow.
Rate of blood flow at the injection site
It is known that if the blood flow in the capillary network to the site of injection and from
there to the capillaries is higher, the rate of absorption of drug would be high. If the drug is
injected into the muscle of the lateral thighs or buttocks, the absorption of drug would be
less and slow; because of less vascularity and higher fat content. When the drug is injected
in the deltoid muscles, absorption of drug would be comparatively higher. Factors that
increase the blood flow such as exercise, increase absorption of drug after intramuscular or
subcutaneous injection. On the other hand, factors that delay blood flow, such as epinephrine
(vasoconstrictors), when administered concurrently at the site of injection, decrease the rate
of drug absorption.
Degradation of drug at the injection site
The distribution of drug may be retarded if the drug is metabolized or degraded at the site of
injection.
Particle size of the drug
The size of the suspended drug particles can influence the rate of dissolution of the drug in
its dosage form vehicle. If the size of the suspended particle is larger, the rate of dissolution
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would be slower, since less surface area of the drug becomes available for interaction with
the body fluids. The precipitated particles may dissolve ultimately, but the rate of dissolution
would be slow.
Formulation ingredients
The materials those are added to the formulation for different reasons such as cellulose
derivatives for suspendability, glycerin for solubilization, antioxidants for improvement of
stability, can potentially affect the distribution of drug from the site of administration. These
effects may be apparent in different ways, such as complexation reduces the rate of drug
dissolution and increased viscosity can slow down the passage of drug from the site of
injection to the systemic circulation.
Manufacturing
Manufacturing of a parenteral formulation involves the mixing of one or more ingredients
with a drug and a suitable vehicle to improve the convenience, acceptability, or effectiveness
of the formulation. Only when a liquid preparation is either not stable or possible to
formulate, dry sterile powder is dispensed. Drug is a chemical compound having definite
physical and chemical properties, it is necessary to screen the excipients and investigate for
any interaction, before mixing them. If any interaction occurs, the formulation requires to be
modified. As such preparation of a sterile formulation is very challenging
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.
In case of a new therapeutically active compound, the amount of information available to the
formulator regarding the physical and chemical properties of the compound and its
interaction with other compounds, sometimes, may appear insufficient. As regards the new
compound, information about the basic properties such as purity, molecular weight,
solubility, colligative properties, and chemical reactivity must be known. Improvement in a
formulation is a continuous process because important properties of a drug or of its product
cannot be known unless the drug product has been stored or used for a long period of time.
Because of the extensive test documents are required by the USFDA, only the outstanding
formulations would be allowed to continue the marketing the product. The major excipient
for parenteral product is the solvent or vehicle; others are antioxidants, preservatives (for
SVPs), solubilizer, mild viscosity imparting agents, buffers, etc.
Solvent system
Most of the parenteral preparations are solutions. If it is aqueous, the solution should be
physiologically compatible with body tissues, and the biological response to be exhibited
should be logically predictable.
The universal solvent, water has high dielectric constant and hence, can dissolve
electrolytes. It can form hydrogen bonds with the organic compounds such as alcohols,
aldehydes, ketones, and amines. On the other hand, it can poorly dissolve nonpolar
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compounds such as alkaloidal bases. In fact, nonpolar substances are soluble in nonpolar
solvents. The drug substances (therapeutically active compounds) administered by injection
may be highly polar to nonpolar; accordingly the polarity of the solvent should be used to
dissolve the drug so that a complete solution is achieved
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.
Therefore, a solvent selected or used for injection must be of low toxicity to body tissue.
Sometimes, to achieve required solubility cosolvents such as ethanol is used. For example,
40% ethanol in water is used to dissolve digitalis glycosides. Compounds that are solubilized
in water can undergo degradation such as hydrolysis, oxidation, decarboxylation, and
racemization.
In such cases, formulation should be designed in such a way that the degradative effects are
as minimum as possible. In most cases the pH of the solution becomes highly affected;
hence, pH is also required to be maintained to reduce degradation. For example, in solution
epinephrine undergoes racemization and oxidation, if the pH of the solution is maintained at
3.0 or less, little reaction can occur. Oxidative degradation can be avoided by replacing
dissolved oxygen by an inert gas such as nitrogen and by adding 0.1% sodium
metabisulphite as an antioxidant. Atropine sulphate in water rapidly hydrolyzes; this can be
avoided significantly by adding a suitable buffer to maintain pH at about 3.5 to 4.0.
Sometimes, the mixed solvents can reduce the degradative reaction. For example, derivatives
of barbituric acid hydrolyze readily in water, particularly at low pH; but by dissolving
pentobarbital sodium in a mixed solvent system containing 60% polyethylene glycol 400 and
10% ethanol in water at pH of about 8.0, the solution can be made stable. However,
degradation reactions can be avoided by using anhydrous, nonpolar solvent such as fixed oil.
In cold seasons, oleaginous injections cannot be used due to their viscosity.
Additives
To achieve required stability and therapeutic efficacy, various additives such as antioxidants,
antibacterial agents (preservatives), buffers, and tonicity modifiers are added to injection
formulations. In some cases, chelating agents such as tetra sodium or calcium disodium salt
of ethylenediamine tetra acetic acid may be added to the formulations to bind the free heavy
metals which can catalyze the degradation reactions. Most commonly the above chelating
agent is used in a concentration of about 0.05%. For example, this chelating agent is used to
stabilize thimerosal in poliomyelitis vaccine. Thimerosal is used as bacteriostatic agent in
the vaccine but it is not stable in the presence of cupric ions. If thimerosal degrades, its
degradation products destroy the antigenicity of the vaccine. Thus, stabilization of
thimerosal means stabilization of vaccine. Sometimes, heavy metals leached out from the
rubber closure can be bound by the chelating agent, and hence can reduce the chance of
interaction between the product and rubber closure.
In case of suspensions of a compound can be stabilized by adding slightly soluble salt
through common ion effect. For example, procaine hydrochloride reduces the solubility of
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procaine benzylpenicillin and helps to stabilize the crystals in aqueous suspension of the
antibiotic.
Sometimes, complexation takes place between the added ingredient and macromolecule in
the formulation. For example, methyl and propyl parabens (preservatives) can form complex
with polysorbate 80, and decrease the antibacterial activity. Hence, the preservative
efficiency is reduced. The preservative efficiency can be regained by compensating the
quantity of preservative bound with non ionic surface active agent. The manufacturing
process consists of all the steps involved starting from accumulation of data to packaging of
finished product and making ready for distribution. Personnel are intimately associated with
these processes and they complete the processes using the facilities available or provided for
operation. Ideally, planned processes can be completed ineffective by the personnel who do
not possess the right attitude and training, or by utilizing the facilities that do not provide an
effective and controlled required environment.
To assure successful manufacturing operations, all process-steps must be written after being
revealed to be effective. All these steps when made available as written methods, these are
called standard operating process (SOPs). These standard operating procedures (SOPs) need
to be approved by the authority and cannot be changed without any permission and
justification. For any change in the original SOPs to be made, permission from the authority
would be required with proper justification. According to the FDA’s Good Manufacturing
Practices, the documented evidences to be produced indicating that these SOPs have been
followed critically and the quality of finished product are as per specification. In fact, inprocess control is essential to assure the quality of the product. In-process quality control is
more significant than the final testing of a finished product. The production of a quality
product is the outcome of continuous, dedicated effort in developing, performing, and
compliance with the SOPs by the QA, Production and QC personnel within the
manufacturing house. A flow diagram for each product is to be provided to improve
observation how the materials are being moved during the manufacturing process. A typical
flow diagram for material movement is shown in Fig 1.12.
Fig. 1.12 Typical flow diagram of materials in manufacturing department
The first step is to collect all materials (raw and packaging materials, equipment) necessary
for a particular batch as per the formula from their respective storage area. Of course, all
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these materials are approved and released for use. According to the master formula or batch
formula the ingredients are mixed or compounded in a desired or required environment so
that highest degree of cleanliness and safety can be maintained. In case of a solution, the
bulk solution is filtered in such a way that it becomes free from bacteria. That is, it is filtered
first through a filter press and then through a membrane filter. The filtered solution must
reach to the filling room maintained aseptic. The process equipment and containers used in
manufacture of the product must be thoroughly cleaned according to the cleaning process for
meeting the specifications.
Process equipment and container components are cleaned thoroughly according to the
cleaning process guidelines. All these should meet the required specifications, are assembled
under a clean environment. If suitable, the materials and depyrogenated before use.
All equipment and supplies to be used in filling area must be sterile. It would be better to
have one door of a double door sterilizer should be facing towards the filling area so that
sterility of the articles could be better maintained. When this is not available, all the articles
sterilized such as hose lines from equipment, other small size articles should be passed to the
filling area after sterilization through as small as possible opening. The opening should be
reclosed immediately after passage of the articles and under aseptic condition so that least
chance of contamination remains there. All the articles for their sterilization should be
wrapped properly. It is recommended that the outer wrapping should be wiped with a
suitable disinfectant solution, since these have been transferred from non-aseptic area to
aseptic area. The sterility of the aseptic area must be maintained all along. The outer
wrappings are loosened, and inner wrappings are opened and contents are received.
Once the filling operation is completed simultaneously sealing is done, so that sterility of the
content of the container is not affected. As shown in Fig 1.14 both filling and sealing areas
are the aseptic; thus, when the product is filled in every container and the container is sealed
thereafter. As per the schedule the sterility of the area should be checked periodically.
Similarly, the cleanliness of the non-sterile areas is checked to ensure the cleanliness as per
specification. The final filled product is then transferred to the packaging area maintained
clean. However, it is necessary to maintain the cleanliness as per the standard maintained in
aseptic room. The packed products are then transferred to quarantine storage area until the
batch is completely tested by QC department and finally approved by QA department after
evaluating all the in-process control test reports. After getting the approval of QA
department, the batch becomes ready for distribution.
Evaluation
Parenteral products include injections and implanted drug products which are administered
through injection. The injections are of following types
Injection (solution)
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1.
2.
Powder for injection or Infusion
Intravenous Infusion – small volume and large volume
Suspension for injections
Emulsions for injection
Irrespective of the type of parenterals the following tests are applied to evaluate parenteral
products. The quality of an injectable is assessed by evaluating the product for following
tests as per the USP. All the following parameters are considered responsible for safety and
therapeutic efficacy of the drug.
Uniformity of content
Extractable volume
Particulate matter in the injections
Bacterial endotoxin present
Presence of pyrogen
Sterility
Uniformity of content & weight: The amount of the active ingredient (drug)present
in each of the 10 containers which have been sampled randomly is analyzed. If all of
the individual values determined are found within 85 to 115% of the stated value, the
sample can be considered to comply with the test. If one value is outside the limits of
75 to 125% of the stated value, the sample would be considered as failed. If one
individual value is outside of 85 to 115% but within 75 to 125 percent of the stated
value, the test is repeated using another 20 containers sampled randomly. The
preparation under investigation complies with the test if among the total sample of 30
containers if only one individual value is outside the limits of 85 to 115 percent and
none are outside the limits of 75 to 125 percent of the stated value. The limits for
uniformity in weight as per the USP are shown in table 1.13.
Table 1.13 Limits for uniformity in weight
Parenteral formulation Stated mass (mg) Percentage deviation (%)
Powders for parenteral use More than 40 10
Powders for eye drops Less than 300 10
Powders for eye lotions 300 or more 7.5
Extractable volume
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3.
Method I: In this test 6 containers are to be used, when the nominal volume is within
5ml; 5 containers for the tests and 1is used for rinsing the syringe. A syringe with
appropriate capacity is rinsed with the sample and then, the content from each
container is withdrawn as much as possible, transferred into a dry graduated cylinder
of such capacity that the total combined volume to be measured occupies not less than
40% of the nominal volume of the cylinder. During each transfer the needle is not
emptied. The process is repeated until the contents of the 5 containers have been
transferred and the average volume of the content is measured. The average volume of
the content of the 5 containers should be within the 100% to 115% of the nominal
volume. Alternatively, the volume of contents in milliliter can be calculated by
dividing the mass (grams) by the density (gm/ml).
Method II: This method is used when the nominal volume is more than 5ml.The
content of not less than 3 containers is transferred separately into a dry graduated
cylinders as stated above so that the volume to be measured occupies not less than
40% of the nominal volume of the cylinder and the volume transferred is to be
measured. The contents of each container should not be less than the nominal volume
and not more than 110% of the nominal volume.
Particulate matter in injections: The test for particulate matter can be alternatively
called the test for clarity. The test is done to detect the presence of any particulate
matter, either floating or sedimented. In solution injections and parenteral infusions
the particulate matter represents extraneous mobile undissolved particles, not any
bubble of air/gas, present in the solutions unintentionally. Solutions for injection to be
administered by the intramuscular or subcutaneous route must meet the requirements
of Particulate Matter in Injections. For indefinite period this requirement has been
postponed for products for veterinary use.
The parenterals packed and labeled exclusively for use as irrigating solutions are also
exempted from the requirements of Particulate Matter in Injections.
Radiopharmaceutical preparations are also exempted from this test.
When the parenteral products (injections) require final filter before administration are
exempted from the tests for Particulate Matter , provided that scientific data are
available to justify this exemption. Method: Before opening, wash the outer surface of
the container by using particle free water-jet; remove the closure carefully so that no
contamination could occur. Mix the contents by inverting the container slowly for 20
times successively. Stop the bubbling of the gas by suitable method such as keeping
the sample undisturbed for 2 min or by sonication. For large volume parenterals,
single unit may be sufficient for the test; while for small volume parenterals, a mixture
of 10 units or more that makes a volume of 25 ml may be taken for the test. The
contents are mixed in a clean container. The test solution can be prepared by mixing
the contents of a suitable number of units such as vial or ampoules and diluting to 25
ml with particle free water or with particle free solvent, if particle-free water is not
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